Derocq J M, Casellas P, Laurent G, Ravel S, Vidal H, Jansen F
Department of Immunology, Sanofi Recherche, Montpellier, France.
J Immunol. 1988 Oct 15;141(8):2837-43.
The in vitro killing of the human CEM cell line was studied by using ricin A-chain immunotoxins constructed with either the whole IgG or the Fab and F(ab')2 fragments of the same T101 (anti-CD5) antibody. In the presence of ammonium chloride as an activator, the "whole" immunotoxin as well as the "fragment" immunotoxins did not show any significant difference in the cell killing efficacy. In contrast, without the activator, the efficacy of the T101 immunotoxin was greatly improved when fragments were used. Indeed, at a saturating dose, a cytoreduction of three orders of magnitude was obtained with the fragment immunotoxins vs less than one order of magnitude for the whole immunotoxin, as assessed in a clonogenic assay. This enhancing effect was related to better cell killing kinetics, because with a similar amount of A-chain molecules bound per cell, T101 fragment immunotoxins achieved a twofold faster protein synthesis inactivation rate than the corresponding whole IgG immunotoxin. No significant difference in activity was shown between monovalent (Fab) and divalent (F(ab')2) forms of fragment immunotoxins. The observation that T101 fragment immunotoxins were more potent than intact immunotoxins was extended to another fragment immunotoxin constructed with an antibody (F111.98) directed against a different epitope of the CD5 Ag. In another model (anti-CD22 1G11 antibody on Raji cells), the fragment immunotoxin did not show any superiority over the IgG immunotoxin which was by itself very potent, strongly suggesting an Ag-dependent phenomenon.
利用由同一T101（抗CD5）抗体的完整IgG或Fab及F(ab')2片段构建的蓖麻毒素A链免疫毒素，研究了其对人CEM细胞系的体外杀伤作用。在氯化铵作为激活剂存在的情况下，“完整”免疫毒素以及“片段”免疫毒素在细胞杀伤效力上没有显示出任何显著差异。相比之下，在没有激活剂的情况下，使用片段时T101免疫毒素的效力有了很大提高。实际上，在克隆形成试验中评估，在饱和剂量下，片段免疫毒素可使细胞减少三个数量级，而完整免疫毒素则不到一个数量级。这种增强作用与更好的细胞杀伤动力学有关，因为在每个细胞结合的A链分子数量相似的情况下，T101片段免疫毒素实现蛋白质合成失活的速率比相应的完整IgG免疫毒素快两倍。片段免疫毒素的单价（Fab）和二价（F(ab')2）形式之间在活性上没有显示出显著差异。T101片段免疫毒素比完整免疫毒素更有效的观察结果扩展到了另一种用针对CD5抗原不同表位的抗体（F111.98）构建的片段免疫毒素。在另一个模型（Raji细胞上的抗CD22 1G11抗体）中，片段免疫毒素没有显示出比本身就非常有效的IgG免疫毒素有任何优势，这强烈表明这是一种抗原依赖性现象。
